Google aims to make electricity derived from the wind and sun and other renewable sources of energy cheaper than burning coal, and the Web search giant has pledged hundreds of millions of dollars toward the effort, including tens of millions in 2008. It didn’t release specific figures, but it did set the goal of producing enough electricity to power San Francisco in “years not decades.”

The initiative will focus first on solar thermal power, wind power and geothermal systems.

Depending on how fast Google spends its money, its investment could rival the federal government’s investment in renewable energy. A Government Accountability Office report found that Department of Energy spending on research and development of biomass, wind and solar energy sources totaled just $65 million in 2006. (Since this was posted this morning, the folks over at reddit have identified other Department of Energy budget documents that make the GAO estimate seem far too low, with $1.16 billion being appropriated for energy efficiency and renewable energy in 2006, and $1.24 billion requested for 2008.)

The Google initiative will create jobs, though how many is unclear. It’s the latest sign that renewable energy technology development can be a growing source of economic power in the coming years.

“If we meet this goal,” said Google co-founder Larry Page, “and large-scale renewable deployments are cheaper than coal, the world will have the option to meet a substantial portion of electricity needs from renewable sources and significantly reduce carbon emissions. We expect this would be a good business for us as well.”